Process for removing acid components from hydrocarbon distillates



Patented Aug. 20, 1940 PROCESS FOR REMOVING ACID COMPO- NENTS FROMHYDROCABBON LATES DISTIL- David Louis Yabrofl', Berkeley, Calif.,asslgnor to Shell Development Company, San Francisco, Calif., acorporation of Delaware No Drawing. Application February 7, 1939, SerialNo. 255,104

9 Claims.

This invention is a continuation-in-part of my co-pending applicationSerial No. 102,893, filed September 28, 1936, which has issued as U. S.Patent 2,152,166, March 28, 1939, and deals with the removal of weaklyacid reacting organic substances from solutions in certainwater-insoluble organic liquids by extraction with aqueous solutions ofcaustic alkali containing a solubility promoter for these substances,and more particularly deals with the removal of mercaptans fromhydrocarbon distillates.

It is frequently necessary to eliminate small quantities of organicrelatively weak acid reacting components such as mercaptans, phenols,thiophenols, alkyl phenols, fatty acids, etc., from their solutions inneutral or weakly basic reacting organic liquids which are substantiallyimmiscible with water such as the liquid hydrocarbons derived frompetroleum, benzene, toluene, xylene, substituted normally liquidhydrocarbons which are substantially insoluble in water, for instance,chlorinated hydrocarbons, of which chlorethane, ethylene dichloride,trichlorethylene, carbon tetrachloride, chlorpropane, chlorbutylene,chlorbenzene, brombenzene, are examples; or nitrogen containinghydrocarbons such as amyl or higher amines, aniline, water-insolublepyridine derivatives, petroleum bases, etc

In order that the water-insoluble organic liquids may be treated by myprocess, they must be substantially inert and resistant to chemicalreaction with strong aqueous solutions of caustic alkali when contactedtherewith for short periods of time, e. g., about 10 minutes or less atnormal room temperatures.

My invention comprises extracting organic acids which are diflicult toextract, such as the weak acids having dissociation constants lower thanthose of fatty acids, e. g., mercaptans, phenols, etc., contained inwater-insoluble organic liquids which are substantially inert towardstrong aqueous caustic alkali solutions at normal room temperatures,with an aqueous solution of caustic alkali in which is dissolved asubstantial amount of a solubility promoter for weak organic acids,under conditions to absorb at least a major portion of the weak organicacids in the aqueous solution, and to form two layers and separating thelayers.

In the application Serial No. 102,893, filed September 28, 1936, I havedisclosed that certain polar substances which are at least partlymiscible with aqueous solutions of strong caustic alkali, promote thesolvent power for weak organic acids of aqueous caustic alkali solutionsin which they are dissolved. I have shown that among other compounds,certain glycerine derivatives, including mono methyl glyceryl ethers arehighly effective in the matter of promoting the solubility of weakorganic acids such as mercaptans, phenols, etc., in aqueous causticalkali solutions. According to the present invention, I use mono methylglyceryl oxy ether or mono methyl glyceryl thioether as solubilitypromoters.

Aqueous solutions of various caustic alkalis may be used. The alkalimetal hydroxides are most useful and effective, although ammonia,alkaline earth hydroxides, quaternary ammonium bases, alkali metalcarbonates, etc., may also be suitable.

The concentration of the aqueous caustic alkali may vary within widelimits. In general, I prefer to use caustic alkali solutions which areabove about 2 normal and preferably between 4 to 10 normal, calculatedon the total solution, although higher and lower concentrations may beused.

Concentration of the glyceryl ether in the aqueous solution shouldpreferably be between about 25 and Moreover, the amountof water in thesolution should be not less than 15% and not more than 70%, preferablynot more than 50%. The presence of water in the above amount is highlydesirable because otherwise the regeneration by steam stripping of spentalkaline solution containing solubility promoter and absorbed weakorganic acids is extremely difficult. Thus steam consumption is greatlyreduced by the presence of the preferred amounts of water, while on theother hand, the extraction eificiency for the weak acids need not bereduced materially. The presence of amounts of water greater than 15%does not cause a substantial hydrolysis of dissolved alkali salts of theweak organic acids as has been supposed by earlier investigators, thehydrolysis being largely a function of the alkalinity of the aqueoussolution.

While increasing the amount of water may have the additional advantageof reducing losses of the glyceryl ether" due to its being dissolved inthe organic liquid, this is a minor consideration when treatinghydrocarbon liquids, because the mono methyl glyceryl ethers aresubstantially insoluble in hydrocarbon liquids even in the presence ofamounts of water much smaller than 15%. Thus, for example, whencontacting isooctane with 20 volume percent of aqueous solutions of monomethyl glyceryl oxy ether containing 10 and 15% water, respectively, andanalyzing the resulting isooctane for the glyceryl K concentration ofmercsptans in aqueous phase concentration of mercaptans in oil phaseSolubility promoter K value None. 507 glycerlne 50; mono methyl glyceryloxy ether...

50 a mono methyl glyceryl thloether The temperature of the extraction ispreferably kept between 0 and 60 0., the extraction emciency decreasingwith increases in the tempera- V ture; and at temperatures below about 0C. difficulties are frequently encountered due to precipitation of aportion of the solubility promoter and/or excessive viscosity of theaqueous caustic alkali containing the solubility promoter.

The extraction of the organic acids from their solutions in the organicliquids described before may be carried out by simply mixing! thesolution with a predetermined amount of the aqueous caustic alkalisolution in which is dissolved a substantial amount of the glycerylether, and then separating the liquids. The resulting aqueous solutioncontains most of the glyceryl ether and the major portion of the organicacids, while the organic liquid stripped from the acids contains a traceof the ether. By washing the stripped organic liquid with water, theglyceryl ether is re-extracted by the latter. The aqueous solution soobtained may then be added to the caustic alkali solution containing thebulk of the ether, and excess water may be separated from the resultingsolution by distillation.

More throrough extraction may be had, however, in a multi-stagecountercurrent extraction system or in a packed tower.

The amount of aqueous caustic alkali solution required in the extractionis normally above about 5% by volume and for economical reasons seldomexceeds about 100% by volume. Normally from about 10 to 50% by volume isused depending upon the required thoroughness of removing the weakorganic acids.

Spent aqueous caustic alkali solution containing the glyceryl ether andweak organic acids may be regenerated by distillation, steaming and/oroxidation, according to well-known principles.

The following example further serves to illustrate my process:

A West Texas straight run full range gasoline containing .1153%mercaptan sulfur was extracted with 10% by volume of a 2.5 normalaqueous caustic solution. 12.7% of the mercaptan sulfur was removed. Thesame gasoline was then treated under identical conditions with 2.5normal aqueous caustic soda solution containing 50% mono methyl glyceryloxy ether. 20.1% of the mercaptan sulfur was removed.

I claim as my invention:

1. In the process of separating organic acid reacting substancescontained in a water-insoluble neutral or basic organic liquid, thesteps comprising treating said liquid with an aqueous solution of astrong base containing a substantial amount of a dissolved mono methylglyceryl ether, said solution containing from 15% to water, underconditions to absorb at least a portion of said acid reacting substancesin said aqueous solution and to form two liquid layers, one comprisingthe aqueous solution containing absorbed acid reacting substances, andthe other consisting essentially of the treated organic liquid, andseparating the layers. I

2. The process of claim 1 in which the aqueous base solution containsbetween 25% and of the glyceryl ether.

3. The process of claim 1 in which the aqueous base is 2 to 10 normal.

4. The process of claim 1 in which the organic liquid is extracted with5% to of the aqueous base solution containing the glyceryl ether.

5. The process of claim 1 in which the base is an alkali metalhydroxide.

6. The process of claim 1 in which the glyceryl ether is mono methylglyceryl oxy ether.

7 The process of claim 1 in which the glyceryl ether is mono methylglyceryl thioether.

8. In the process of separating mercaptans contained in a hydrocarbondistillate, the steps comprising treating said distillate with at least5 volume percent of a 2 to 10 normal aqueous alkali metal hydroxidesolution in which is dissolved between 25% and 75% of mono methylglyceryl ether, said solution containing from 15% to 70% water, underconditions to absorb at least a major portion of said mercaptans in theaqueous solution and to form two liquid layers, one comprising theaqueous alkali metal hydroxide solution containing substantially all ofthe glyceryl ether and the major portion of the mercaptans, and theother consisting essentially of the treated hydrocarbon distillate, andseparating the layers.

9. In the process of separating organic acid reacting substancescontained in a water-insoluble neutral or basic organic liquid, thesteps comprising treating said liquid with an aqueous solution of astrong base containing a substantial amount of a dissolved compoundbeing selected from the group consisting of mono methyl glycerol oxyether and mono methyl glyceryl thioether. said solution containing from15% to 70% H20, under conditions to absorb at least a portion of saidacid reacting substances in said aqueous solution and to form two liquidlayers, one comprising the aqueous solution containing absorbed acidreacting substances, and the other consisting essentially of the treatedorganic liquid, and separating the layers.

.DAVID LOUIS YABROFF.

